Thanks for your reply.
As I said, the vehicles do eventually get back to their parking positions, but take quite a detour to do so when they could just back up a couple of meters and be done.
I have positioned the belt loaders to face directly towards the cargo doors when the aircraft is parked. The loaders just have to move straight forward a couple of meters (which they do), and when done, move back a couple of meters, driving backwards (which they do after loading, but not after unloading in which case they take a some detour around the plane).
This behavior can be observed e. g. on Aerosoft EDDS professional with the FSL A320 when arriving and parking on Gate 42. This is essentially a totally empty parking spot on the Apron. That parking spot is certainly not cramped, no crates, vehicles, buildings etc. around that come from the airport scenery.
So, if this is solvable by custom vehicle positioning, could you please give me some pointers what to look out for in addition to providing an unobstructed path, which is quite obvious?